1. Field of the Invention
The present invention relates to a machine designed for the manufacture of a multi-layer fibrous web, in particular a paper or carton web, in which the layers produced by respective formers are couched together.
2. Description of the Related Art
A machine designed for the manufacture of a multi-layer fibrous web in which the layers produced by formers are couched together is described in DE 197 33 316 A1.
Several other types of former are known, such as the Fourdrinier former, the hybrid former and the so-called roll-blade gap former. In previous models of the Fourdrinier former, drainage occurs on the wire side. A concentration of fines on the top side is produced by wire mesh edge pulses. In hybrid formers, the primary drainage process occurs on the wire side. The percentage of fines on the top side is reduced by performing the drainage process in the upper wire area on the top side. In roll-blade gap formers, drainage occurs first on the top wire side and then on the bottom wire side, which produces a greater fines content on the bottom wire side. Combinations of two or more gap formers have previously been proposed. Previous embodiments of this format with two gap formers used in the packaging industry have included one system having a so-called DuoFormer Base and DuoFormer Top with the same running direction of the paper web in the sheet-forming process. In that example, the top wire side, featuring a low fines content, is couched together with the lower wire side, featuring a high fines content.
A disadvantage of the embodiments mentioned above lies in the fact that the adhesion between the two layers is too high for certain applications.
The present invention provides a machine for the manufacture of a multi-layer fibrous web. The manufacture of a multi-layer fibrous web is accomplished by feeding into the relevant couching zone at least two layers that are to be couched together, each having a lower fines content on one side, in such a way that they come into contact with each other on the sides having lower fines content. In this process, at least one of the two layers is generated by a gap former.
The present invention produces a multi-layer fibrous web with reduced adhesion between the two layers, allowing the deliberate separation of one layer of the sheet without causing the destruction of the remaining layer. A further advantage is achieved with regard to a possible alteration of the properties of the paper in terms of porosity, roughness, penetration and printing characteristics.
At least one gap former is included in the present invention, having a forming element on which a fibrous web layer is formed with higher fines content on the side of the layer facing the forming element. The forming element is preferably a forming roll.
In an embodiment of this invention, a first gap former is provided to produce a first layer and a second gap former is provided to produce a second layer. In this case, the first layer is fed by the bottom wire of the first gap former, which is separated from the top wire into a couching zone, where the sides of lower fines content of the two layers are couched together.
For practical purposes, the direction of rotation of the forming element in the second gap former is set against the direction of rotation of the forming element in the first gap former. The second layer is reversed in this case by a couch roll provided in the area of the couching zone.
In certain cases it may be advantageous for the machine to be provided with at least one Fourdrinier former, in which the sheet-forming process of the layer is effected with a higher fines content on the top side facing away from the machine wire.
In one embodiment of this invention, one Fourdrinier former is provided to produce a first layer and a second Fourdrinier former to produce a second layer, whereupon these two layers are couched together with the sides of higher fines content of each layer coming together in a first couching zone. In addition, a gap former is provided to produce a third layer, whereupon the second and the third layers are couched together with the sides of lower fines content of each layer coming together in a second couching zone.
For practical purposes, the jet direction of the headbox in the second Fourdrinier former is generally set against the jet direction of the headbox in the first Fourdrinier former. The second layer is reversed in this case by a couch roll provided in the area of the first couching zone. The third layer is, by preference, reversed by a couch roll provided in the area of the second couching zone.
In a further embodiment of this invention, one gap former is provided to produce a first layer and two Fourdrinier formers are provided to produce a second and a third layer, respectively. In this case, the second and the third layers are couched together with the sides of higher fines content of each layer coming together in a first couching zone, and the first and the second layers are couched together with the sides of lower fines content of each layer coming together in a second couching zone.
For practical purposes in this case, the jet direction of the headbox in the Fourdrinier former, which produces the third layer, is generally set against the jet direction of the headbox in the Fourdrinier former which produces the second layer.
In a further embodiment of this invention, one Fourdrinier former is provided to produce a first layer, and two gap formers are provided to produce a second and a third layer, respectively. In this case, the first and the second layer are couched together with the sides of higher fines content of each layer coming together in a first couching zone, the resulting fibrous web and the third layer are couched together with the sides of lower fines content of each layer coming together in a second couching zone.
For practical purposes in this case, the jet direction of the headbox in the gap former, which produces the second layer, is generally set against the jet direction of the headbox in the Fourdrinier former which produces the second layer. In a like manner, the jet direction of the headbox in the gap former which produces the third layer is generally set against the running direction of the first layer and the running direction of the second layer.
In a further embodiment of this invention, two gap formers are provided to produce a first and a second layer, respectively, and one Fourdrinier former is provided to produce a third layer. In this configuration, the first and the second layer are couched together with the sides of lower fines content of each layer coming together, and the second and the third layer are couched together with the sides of higher fines content of each layer coming together.
For practical purposes in this case, the jet direction of the headbox in the gap former, which produces the second layer, is generally set against the running direction of the first layer. In a like manner, the jet direction of the headbox in the Fourdrinier former which produces the third layer is generally set against the running direction of the first layer and the running direction of the second layer.
In a further embodiment of this invention, a gap former is provided to produce a first layer, a Fourdrinier former is provided to produce a second layer and another gap former is provided to produce a third layer. In this configuration, the first and the second layer are couched together with the sides of lower fines content coming together, and the second and the third layer are couched together with the sides of higher fines content coming together.
For practical purposes in this case, the jet direction of the headbox in the gap former which produces the second layer is generally set against the running direction of the first layer. In a like manner, the jet direction of the headbox in the Fourdrinier former which produces the third layer is generally set against the running direction of the first layer and the running direction of the second layer.
Each gap former may be equipped with either a single-layer or a multi-layer headbox.
Where required, constant pressure drainage elements can be provided for web drainage purposes. These may be used in combination with any of the formers. An example describing how they may be implemented can be found in document DE 197 33 316 A1.